KR20210034670A - Sensor for electronic detection - Google Patents

Abstract

The present invention relates to a sensor for the detection of electrons emitted from an object to be used with a charged particle beam column operated at a specific column and wafer voltage. The sensor is configured and operable to minimize electronic energy loss while at least reducing the interaction of negative ions with the active region of the sensor. The sensor is also configured and operable to minimize both the gradual deterioration of the cathodic emission efficiency of the active region, and the dynamic change in cathodic emission that occurs during operation of the sensor and progresses throughout the life of the scintillator.

Description

Sensor for electronic detection

The present invention relates to the field of radiation scintillation detectors. More specifically, the present invention relates to a scintillation-based sensor structure useful for electronic detection.

Scintillators are materials that absorb radiation and generate fluorescence when radiation such as alpha rays, beta rays, gamma rays, X-rays, or neutrons strikes. The scintillator can be combined with a photodetector, such as a photomultiplier tube, to constitute a radiation detector. Luminescent materials, when struck by an incoming particle, absorb that energy and emit a flash (ie, re-emit the absorbed energy in the form of light). Various systems, such as scanning electron microscopes (SEM) and electron beam inspection tools, can include a scintillator and a light guide. There is a growing need to provide reliable high-speed scintillators with long life.

An object can be evaluated (measured, inspected, and/or reviewed) by illuminating the object with electrons. Then, secondary electrons or back-scattered electrons BSE reflected and/or scattered from the object are detected. Accordingly, the scintillator is bombarded with secondary electrons or back-scattered electrons under a certain accelerating voltage, and thus emits detectable light by cathodoluminescence (CL). Light is substantially collected by the light guide. Photons generated inside the scintillator are emitted in all directions, and undergo reabsorption and total internal reflection due to the scintillator and the refractive index of the substrate. When the scintillator-light guide method is used as a detector, one of the tasks to be considered in its design is to maximize the transfer of photons to the light guide. For this purpose, the surfaces of the scintillator are coated with a coating to reflect the photons back to the scintillator.

The inventors have surprisingly found that the scintillator is also impacted by negative ions. These negative ions are substantially accelerated toward the scintillator, which in turn causes a deterioration in the efficiency of the scintillator. This damage mechanism is extremely efficient and occurs within a very short period of time and, if not mitigated, causes immediate and irreversible deterioration of the scintillator. The source of the anions is contaminants and hydrocarbons on the imaged sample or wafer and not on the scintillator. Since negative ions are formed by a process known as electron stimulation desorption (ESD), their presence is inherent in scanning electron microscopy (SEM) imaging of samples. Negative ions reach the scintillator due to the field distribution in the SEM.

In order to solve this problem associated with the impact of negative ions, the present invention provides, among other things, a sensor having a coating structure bordering the scintillator structure, which is exposed to electrons emitted from an object. The coating structure is configured to have a specific thickness selected to minimize electronic energy loss when colliding with the coating structure while at least reducing the interaction of anions with the active region. The term “at least reduces the interaction of anions” refers to slowing and inhibiting the path of anions within the coating structure such that the anions do not reach the scintillator active region. In this way, the coating structure prevents the anions from damaging the scintillator material (ie, the active area) by at least reducing (eg, completely removing) the interaction of the anions with the scintillator structure.

The coating structure is also intended to create a contact to the bias electrode. This provides an accelerating voltage for the secondary and BSE electrons and closes the electrical loop of the current carried by the secondary electrons as well as the incident beam. The coating structure is constructed and operable to maintain a uniform potential across the interface between the coating structure and the active region of the scintillator structure (ie, homogenization of the potential across the sensor) and/or to improve electrical contact. The coating structure may have a planar shape, which may or may not be continuous. For example, a structure having a lattice shape can be used. Moreover, the coating structure is created inside the scintillator to reflect photons emitted by the active area back towards the active area (i.e. to maximize the output of the photons to the light guide connected on its rear side to the scintillator). It has a specific material composition that is chosen to reflect back the photons that become.

Accordingly, in accordance with a broad aspect of the present invention, a sensor for detection of electrons emitted from an object is provided to be used with a charged particle beam column operated at a specific column and wafer voltage. The sensor includes an active area and a scintillator structure with a specific lifetime. The scintillator structure includes a high-speed scintillator material (e.g., having an attenuation time of approximately ns) and operable to emit photons of a specific wavelength range upon collision of electrons of a specific collision energy by cathode ray emission, and a scintillator structure. It includes a coating structure that forms a boundary and is exposed to electrons emitted from the object. The coating structure is constructed and operable to maintain a uniform potential across the interface between the active region and the coating structure. The coating structure has a specific material composition selected to reflect photons emitted by the active area back towards the active area. The coating structure also has a specific thickness selected to minimize electronic energy loss when colliding with the coating structure while at least reducing the interaction of anions with the active region.

In some embodiments, the scintillator structure includes a semiconductor group III-V multiple quantum well structure.

In some embodiments, the specific thickness is determined by the energy at which negative ions interact with the active region depending on the specific column and wafer voltage.

In some embodiments, the thickness is selected according to the type of anions damaging the active area.

In some embodiments, the coating has a thickness of at least 200 nm.

In some embodiments, a particular material composition includes a conductive material in which the coating structure is configured and operable as an electrode that applies a potential that accelerates secondary and backscattered electrons towards the sensor.

Unfortunately, damage to the scintillator structure is not exclusively related to negative ion bombardment. The direct impact of the scintillator with secondary electrons or backscattered electrons causes deterioration of the luminous efficiency of the scintillator after a certain dose. This also causes a dynamic effect of varying the scintillator light output over a short period of time (a measure of image capture). For example, the deterioration of the efficiency of the scintillator can ^{reach 50% after a dose of 0.3 C/cm 2} and in some cases even 90%.

In order to solve the above-mentioned problems associated with the gradual deterioration of the cathodic emission efficiency of the active region, and the dynamic change in cathodic emission that occurs during the operation of the sensor and progresses throughout the life of the scintillator, the present invention provides a multi-coating structure. It provides a coating structure comprising a. The multi-coating structure defines a profile with different physical and chemical properties along its depth. Different physical and chemical properties along the depth of the multi-coating structure include a specific material composition and a specific thickness. The above-mentioned properties are chosen to minimize both the gradual deterioration of the cathodic emission efficiency of the active region and the dynamic change in cathodic emission that occurs during operation of the sensor and progresses throughout the life of the scintillator. Losses in optical mode due to two factors: transmission of secondary and backscattered electrons through the coating structure (effective excitation level), and absorption in the coating structure or at the interface between the scintillator structure and the coating structure. It affects the optical intensity of cathode ray emission. The material composition of the coating structure is selected according to the interfacial chemistry between the coating material and the scintillator material on which the coating material is deposited. The reflectance/absorption of the coating structure material with respect to the operating wavelength is considered. If the reflectivity of the coating at the emitted wavelength is high, the scintillator efficiency is improved and vice versa is also possible. The coating structure can passivate the surface states and homogenize the surface potential to form a good equipotential interface. The use of different materials affects the contact, the chemistry of the interface between the coating structure and the scintillator structure, and the degree of homogenization of the surface potential and the passivation of the defects terminating at the scintillator structure surface. ) Makes it possible to appropriately control the formation of.

In some embodiments, the multi-coating structure may include at least two different coating materials with different reflection coefficients in a specific wavelength range of the emitted photons. The multi-coating structure can be made of at least two layers. The two layers can have different thicknesses.

In some embodiments, the multi-coating structure may include a first reflective material bordering the active area, and a second reflective material bordering electron emission from the object. The first reflective material has a lower reflection coefficient than the second reflective material. The first reflective material bordering the active area may be selected to enable good ohmic contact (ie, low resistance) to mitigate the effect of at least one of surface conditions, defects, and electron traps. The second reflective layer may have a thickness selected according to the type of anions that damage the scintillator structure. Accordingly, the present invention provides a sensor for detection of electrons emitted from an object, which is configured to have an increased lifetime. The term "lifetime or lifespan" refers to both the rate of decrease in the efficiency of the scintillator and the stability of the efficiency/output of the scintillator (ie, the dynamic transition effect described above). A sufficiently long life (related to the dose to accumulate according to specific operating conditions), and the stability of the scintillator output without transition effects are important parameters for the performance of the scanning electron microscope.

According to another broad aspect of the present invention, a sensor for detection of electrons emitted from an object is provided for use with a charged particle beam column operated at a specific column and wafer voltage. The sensor includes an active area and a scintillator structure with a specific lifetime. The scintillator structure includes a high-speed scintillator material configured and operable to emit photons of a specific wavelength range upon collision of electrons of a specific collision energy by cathode ray emission, and a multi-coating structure bordering the scintillator structure. The term “multi-coating structure” refers to a structure having different physical and chemical properties, such as material, reflection coefficient, thickness, chemical properties, conductivity, etc. along its depth. In particular, both the thickness and the material of the multi-coating structure are specifically configured to solve the lifetime problem described above and optimize the efficiency. The change in reflective properties can be continuous, or a multi-coating structure can define two geometric regions with different reflective properties. In other words, the multi-coating structure may comprise at least two different coating materials with different reflection coefficients in a specific wavelength range of the emitted photons.

The top surface of the multi-coating structure bordering the scintillator structure, and the bottom surface of the multi-coating structure both receive electron-charged particle emission from the object. Thus, the bottom surface of the multi-coated structure (opposite the surface bordering the scintillator structure) is configured to be exposed directly to the environment (eg, vacuum) to receive the emission of electronically charged particles from the object. The multi-coating structure/layer can be made of two or more different coating materials, or can be made of one composite material with different physical and chemical specific properties. The multi-coating structure (e.g., a specific material composition) is configured to reflect photons emitted by the scintillator structure back toward the scintillator structure, thereby controlling interfacial properties with the active region of the scintillator structure toward the active region, and Operation is possible. The specific thickness is selected to minimize both the gradual degradation and dynamic effects of the cathodic emission efficiency of the active region (eg, the dynamic change in cathodic emission that occurs during operation of the sensor and advances throughout the life of the scintillator).

In some embodiments, the present invention relates to a sensor for detection of electrons emitted from an object. The sensor consists of a scintillator comprising a scintillator material configured and operable to emit photons upon collision of electrons, and a multi-coating structure bordering the scintillator structure. In this regard, it should be understood that in order to operate the sensor of the present invention, the sensor need not include an additional layer.

In some embodiments, the scintillator structure includes a semiconductor group III-V multiple quantum well structure.

In some embodiments, the multi-coating structure is made of at least two layers. The two layers can have different thicknesses.

In some embodiments, the multi-coating structure comprises two different coating materials, i.e., a first reflective material bordering the active area, and a second reflective material bordering the emission of electronically charged particles from the object. . The first reflective material (ie, the additional coating material) has a lower reflection coefficient than the second reflective material, which is configured to reflect photons back towards the semiconductor scintillator structure. The first reflective material bordering the active area may be selected to enable good ohmic contact to mitigate the effect of at least one of surface conditions, defects, and electron traps.

In some embodiments, at least one of the coating materials is a conductive material that enables the multi-coating structure to be configured and operable as an electrode that applies an electric potential to the sensor. In some embodiments, both materials are conductive.

The ratio between the thickness of the first reflective material and the thickness of the second reflective material may exceed 1:10 or 1:20. The thickness of the first reflective material may be in the range of about 2 to 50 nanometers. The thickness of the second reflective material may be in the range of about 20 to 600 nanometers.

According to another broad aspect of the invention, a method for detection of electrons emitted from an object is provided. The method includes receiving electrons by a scintillator; By the scintillator, emitting photons due to the reception of electrons. Emission of photons includes emitting photons towards a light guide, and emitting photons towards a multi-coating structure bordering the scintillator. The method additionally includes reflecting photons that have passed through the multi-coated structure towards the scintillator by the multi-coated structure. Accordingly, the interface between the scintillator and the multi-coating structure is constructed and operable to be controlled.

According to yet another broad aspect of the present invention, a method is provided to increase the lifetime of a sensor for detection of electrons emitted from an object to be used with a charged particle beam column operated at a specific column and wafer voltage. The method includes providing a scintillator structure having an active region comprising a high speed scintillator material. The method also includes the steps of demarcating a scintillator structure with a multi-coating structure configured to reflect back photons emitted by the scintillator material, and defining different physical and chemical properties along the depth of the multi-coating structure. Includes steps. Additionally, the method includes controlling both interfacial properties (e.g., the gradual deterioration of the cathodic emission efficiency of the active region, and the dynamic change in cathodic emission that occurs during the operation of the sensor and progresses throughout the life of the scintillator. Minimizing), and increasing the lifetime of the sensor.

In some embodiments, the method further includes selecting the materials of the multi-coating structure (eg, selecting at least two materials of the multi-coating structure) and selecting a specific thickness thereof.

In some embodiments, the method further includes removing the interaction of the anions with the scintillator structure. Eliminating the interaction of the anions with the scintillator material may further include selecting the thickness of the multi-coating structure.

In order to better understand the subject matter disclosed herein, and to illustrate how the subject matter disclosed herein may be practiced in practice, embodiments will now be described by way of non-limiting example only, with reference to the accompanying drawings.
1A and 1B show typical cathodic images of undamaged and uniform detector regions.
1C and 1D show cathode ray emission images of ion-damaged regions of the scintillator.
1E illustrates an example of a schematic diagram representing a sensor for detection of electrons emitted from an object and propagation of photons within the sensor, in accordance with some embodiments of the present invention.
FIG. 2A is a photograph showing a cathode ray emission image of a scintillator region showing a region deteriorated and a non-degraded region due to accumulation of doses of electrons striking the scintillator under standard operating conditions.
2B-2C illustrate the degradation and its dynamic effects, respectively.
2D illustrates an example of a sensor for detection of electrons emitted from an object and a schematic diagram representing propagation of photons within the sensor, according to some embodiments of the present invention.
3 illustrates an example of a schematic diagram representing a system to be used with the sensor of the present invention.
4 illustrates a flow diagram illustrating a technique for detection of electrons emitted from an object.
5 illustrates a flow diagram illustrating a technique for increasing the lifetime of a sensor, based on the teachings of the present invention.

As explained above, the inventors have surprisingly found that during operation the scintillator is also impacted by negative ions. 1A and 1B show an imaged area of an object with and without a damaging ion beam, respectively. Such anions are formed near the surface of an object that is impacted by electrons, and are produced by the process of electron stimulation desorption. 1C-1D, negative ions are generated on the surface of the object being inspected and are attracted into the column by electric fields generated by the charged particle beam column. The ions are accelerated by a certain potential and collide with the detector, damaging the detector. Elimination of the interaction of negative ions with the scintillator structure provides stable cathodic light emission during operation and high speed operation.

The present invention makes it possible to provide detector scintillators that are sufficiently immune to ion damage without compromising current performance. This can be implemented by appropriately selecting the thickness and/or material of the coating structure. The coating structure is constructed and operable to prevent ions originating from the surface of the object from reaching the scintillator structure. Accordingly, the life of the scintillator structure is increased, and likewise the life of the sensor is increased. Referring to Fig. 1E, a schematic diagram of a sensor 10 of the present invention configured and operable to detect electrons emitted from an object is illustrated. The sensor 10 has a scintillator structure 12 (e.g., a scintillator film) made of a high-speed scintillator material that is configured and operable to emit photons of a specific wavelength range upon collision of electrons e- by cathode ray emission. ), and a coating structure 14 bordering the scintillator structure 12 and exposed to electrons e- emitted from the object. Photons produced by the scintillator material can propagate in various directions. For example, the photons 73 emitted by the scintillator structure 12 propagate toward the light guide 50 included in the charged particle beam column (shown in FIG. 3). However, some photons as illustrated by 71 are emitted by the scintillator structure 12 in a different direction than that directed towards the light guide 50. Accordingly, the coating structure 14 is configured to have a specific reflective property selected to redirect photons emitted by the scintillator structure 12 propagating toward the coating structure 14 back to the scintillator structure 12. do. In other words, the coating structure has a specific material composition selected to reflect photons emitted by the scintillator material back towards the active region of the scintillator structure. The term "active region" refers to the region in which the scintillator structure exhibits radiation sensitivity. The coating structure 14 also has a specific thickness (T) selected to minimize electron energy loss when colliding with the coating structure 14 while at least reducing (e.g., completely removing) the interaction of negative ions with the active region. It is configured to have. The coating structure 14 allows electrons (such as secondary electrons and/or backscattered electrons) to reach the scintillator structure 12 while substantially preventing negative ions from reaching the scintillator structure 12. It is made thick enough (eg, in the range of several hundred nanometers, for example, about 200 nanometers to 600 nanometers) to allow. In this regard, it should be noted that making the coating structure 14 too thick can reduce the energy of electrons passing through the coating structure 14. However, since the coating structure 14 prevents ionic damage, the thickness T of the coating structure 14 can provide a compromise between the sensitivity of the sensor and its lifetime. The thickness T of the coating structure 14 may be determined based on one or more parameters of the system including the sensor. For example, thinner elements may be required when stopping lower energy negative electrons. When using different potential modalities along the system, it can be obtained that negative ions of lower or higher energy impinge on the sensor. One or more parameters of the system may include any operating condition, any irradiation parameter, any collection parameter, a predefined required life span of the scintillator, and an acceptable amount of anions that can reach the scintillator. . Parameters are also the acceptable percentage of anions that can reach the scintillator, any parameter related to anions and/or any parameter related to electrons detected by the sensor, the identity of anions (e.g., hydrogen anions). , The energy of negative ions upon reaching the sensor, distribution of negative ions upon reaching the sensor, acceleration voltage to direct negative ions toward the sensor, arbitrary parameter of the electrostatic field near the sensor, arbitrary parameter of the immediate magnetic field of the sensor, sensor It may include the energy of electrons when reaching to, distribution of electrons when reaching the sensor, and the like. The thickness T of the coating structure 14 may be selected depending on the type of negative ions damaging the active area. Specifically, as the ions may be heavier or lighter, the coating configurations may change accordingly. After determining that the anions have different identity (e.g., hydrogen), the path of the anions within the coating structure 14 can be measured and/or simulated, and the coating structure 14 will be designed to be thicker than the depth of the path. I can. The coating structure 14 bordering the scintillator structure 12 has the functionality of uniformly distributing a voltage bias applied to the scintillator structure (ie, specific column and wafer voltages) over the surface of the scintillator. Accordingly, the coating structure 14 is constructed and operable to maintain a uniform potential across the interface between the active region and the coating structure.

In this regard, it should be noted that the thickness T of the coating structure 14 must, on the one hand, be properly selected to stop the propagation of negative ions. On the other hand, electrons moving toward the scintillator structure 14 should not be excessively slowed down. In other words, the coating thickness T is, on the one hand, tailored to block ions from reaching the active area. On the other hand, such tailoring minimizes electronic energy losses to maximize efficiency. The reflective efficiency of the coating structure makes it possible to provide electrons with the ability to be evacuated and minimize their entrapment. Moreover, the thickness T can be determined by the energy of the ions striking the sensor. This energy is determined by the scintillator and object potential. In other words, the specific thickness T may be determined by the energy at which negative ions interact with the active region according to a specific column and wafer voltage. The thickness T can also be selected depending on the type of anions damaging the active area. The exact thickness T of the coating structure 14 is determined according to the operating conditions and sensor configuration, and can still be modified to accommodate these conditions within the guidelines mentioned above, in order to alleviate ion problems. In certain non-limiting examples, the coating has a thickness of at least 200 nm for electrons with collision energy in the range of about 9-15 kV.

Moreover, it should be understood that the problems associated with the interaction of anions are of particular importance when high speed scintillator materials are used. Thus, for example, the scintillator structure includes a semiconductor group III-V multiple quantum well structure. For example, the scintillator material may have a heterogeneous structure. For example, the scintillator material may emit in an ultraviolet or blue or yellow spectrum. For example, a semiconductor group III-V multiple quantum well structure may include a nitride semiconductor layer, which refers to a compound containing at least one of Ga, In, and Al as a group III element and containing N as a main group V element. have.

It should be noted that in the drawings, the scintillator structure 12 and the coating structure 14 are illustrated as having a planar shape, but this is only an example. For simplicity and clarity of illustration, it will be appreciated that elements shown in the drawings are not necessarily drawn to scale. The coating structure 14 may be deposited on the scintillator structure 12 by any deposition method (eg, by thermal evaporation). Coating techniques have been well studied, and there are many suitable coatings and layers that can be included in the present invention. Additionally, a number of ways of forming coatings having the optical and/or protective properties required by the present invention are known in the art.

The coating structure 14, although not specifically shown, may be formed by a single material layer or may include a plurality of layers. In some embodiments, the coating structure 14 includes a multi-coating structure, the multi-coating structure having different physical and chemical properties along its depth. The multi-coating structure is configured to have a specific material composition and a specific thickness. They are chosen to minimize both the gradual deterioration of the cathodic emission efficiency of the active region and the dynamic change in cathodic emission that occurs during operation of the sensor and progresses throughout the life of the scintillator. These coatings and sensors of different thicknesses and configurations can even be used in the same scanning electron microscope.

In some embodiments, the multi-coating structure may include at least two different coating materials with different reflection coefficients in a specific wavelength range of the emitted photons. The multi-coating structure can be made of at least two layers. The two layers can have different thicknesses.

In some embodiments, the multi-coating structure may include a first reflective material bordering the active area, and a second reflective material bordering electron emission from the object. The first reflective material may have a lower reflection coefficient than the second reflective material. The first reflective material bordering the surface of the active area is selected to allow good ohmic contact with the surface of the scintillator structure to mitigate the effect of at least one of surface conditions, defects, and electron traps. Can be. The second reflective layer may have a thickness selected according to the type of anions that damage the scintillator structure. Accordingly, the first reflective material and the second reflective material may have different thicknesses. In certain non-limiting examples, the first reflective material can be made relatively thin (eg, in the range of about 3-20 nanometers, eg, 15 nanometers) due to the lower reflection coefficient. However, the thickness of the first reflective material, due to the lower reflection coefficient, should be configured to mitigate the lifetime problem and minimize the reduction in efficiency. In addition, the second reflective material is thick enough to allow electrons (such as secondary electrons and/or backscattered electrons) to reach the scintillator while substantially preventing negative ions from reaching the scintillator structure ( For example, it is made in the range of several hundred nanometers, for example about 200 nanometers to 600 nanometers). In this regard, it should be noted that making the second reflective material sufficiently thick can reduce the energy of electrons passing through the second reflective material. However, since the second reflective material prevents ionic damage, the thickness of the second reflective material can provide a compromise between the sensitivity of the sensor and its lifetime. It should be noted that the first reflective material, or a combination of the first reflective material and the second reflective material, may be configured to substantially prevent negative ions from reaching the scintillator structure. Increasing the thickness of the first reflective material may increase the role of the first reflective material substantially preventing negative ions from reaching the scintillator structure. For example, when the first reflective material is expected to take on the primary role (or exclusive role) of substantially preventing negative ions from reaching the scintillator, the first reflective material may be thicker than the second reflective material. It should be noted that the thickness of the first reflective material and/or the thickness of the second reflective material may be determined based on one or more parameters of the system comprising the sensor. In some embodiments, the second reflective layer has a thickness and/or material that is selected depending on the type of anions that damage the scintillator structure.

As explained above, another problem associated with the deterioration of the luminous efficiency of the scintillator is damage to the scintillator structure caused by secondary electrons or backscattered electrons. Reference is made to FIG. 2A which shows a cathodic emission image of a scintillator structure having a degraded region and a non-degraded region surrounding the degraded region. The deterioration of the efficiency of the scintillator increases with the accumulated electron dose over time. Electron bombardment creates additional defects in the scintillator structure (or enlarges a lower efficiency zone around existing defects), thus reducing the cathodic emission efficiency. More specifically, the accumulated dose of electrons emitted by the object is the deterioration of the scintillator efficiency (i.e., the deterioration of cathode ray emission) and the dynamic/temporal/transition effect (hereinafter referred to as a dynamic effect hereinafter) as the dose increases. ), resulting in a change in cathode ray emission during operation. These two effects reduce the lifetime of the scintillator-based detector. The dynamic behavior is due to two effects: efficiency recovery and efficiency decay-back. Restoration occurs when the scintillator is exposed to the electron flux, and the first exposure time frame (eg, the first frame in multi-frame image capture) exhibits the above degradation, but successive time frames are brighter. After restoration, if no electrons hit the detector, the efficiency decays slowly (eg, approximately a few minutes) back to the degraded value. This process can be referred to as re-attenuation. The process of re-attenuation involves relaxation in the excitation of the carrier in the material with internal defects leading the carriers back to the defect. Reference is made to FIGS. 2B-2C illustrating the deterioration effect. More specifically, the scintillator output in arbitrary units versus the accumulated dose is represented in FIG. 2B as a measure of the accumulated dose. The scintillator output at different current densities as a function of time in arbitrary units is represented in FIG. 2C as a measure of image acquisition. The unwanted dynamic effect of exposing the scintillator to electrons is clearly shown in the figure. The recovery rate and saturation value depend on the current density. Higher current densities saturate the efficiency at higher levels. Higher current density results in faster recovery. Accordingly, the dynamic effect increases with the accumulated dose and is highly dependent on the current density impinging on the scintillator during operation and the short-term history of this current density. More specifically, the dynamic effect may vary depending on the specific investigation and/or collection conditions of the current evaluation iterations, and is also affected by previous evaluation iterations. A constant and stable decrease in the efficiency of the scintillator can be mitigated or compensated for. Conversely, dynamic effects are more difficult to compensate due to the dependencies of the effects mentioned above. The time scale for accumulating this dynamic effect may be a function of the operating conditions of the system including the scintillator, and the range may be, for example, several months to a year of operation. It has been found that the cause of the dynamic effect is the surface conditions at the surface of the scintillator structure. These surface states are derived from the physical properties of the scintillator material and the method of growth thereof, and are intrinsic properties of the scintillator material. In this regard, it should be noted that effects of reducing the lifetime of a scintillator-based detector as described are observed especially for high-speed scintillators.

Referring to Fig. 2D, a schematic diagram of a sensor 10' of the present invention configured and operable to detect electrons emitted from an object is illustrated. According to this broad aspect of the invention, the sensor 10' includes a scintillator structure 12 (eg, a scintillator film) made of a high-speed scintillator material. The scintillator structure 12 is configured and operable to emit photons of a specific wavelength range upon collision of electrons e- by cathode ray emission, and the multi-coating structure 14 borders the scintillator structure. . The present invention provides a sensor for detection of electrons emitted from an object to be used with a charged particle beam column operated at a specific column and wafer (ie, accelerating) voltage, configured to have an increased lifetime.

The inventors have found that different materials and different thicknesses lead to different deterioration and different restorations. Some materials provide maximum efficiency but have the lowest lifetime, and some materials provide low efficiency but have the longest lifetime. Thus, the present invention provides a multi-coating structure with different physical and chemical properties along its depth. The unique combination of the selected material in selected thicknesses provides the sensor with increased lifetime and optimized efficiency. The change in these properties can be continuous, or a multi-coating structure can define two geometric zones with different properties. The multi-coating structure can be made of two different coating materials or one composite material with specific properties (eg, a single material with the properties mentioned above).

In this regard, it should be understood that quantum wells emit photons under excitation. These photons diffuse to fill the volume formed by the entire scintillator structure, and before the photons leave this volume, the photons form internal "modes". The optical mode in the scintillator structure is partially constrained by total internal reflection at the boundaries, but the optical mode also diffuses slightly beyond the interfaces and includes a vanishing portion at the interface between the scintillator structure and the coating structure. These interfaces can be transparent or absorbent. When the interface is transparent, the interface acts as a dielectric cladding (no loss). However, when the interface is absorbent, some of the light emission is not collected by the sensor and is absorbed at the interface. Accordingly, the material composition of the multi-coating structure of the present invention is appropriately selected to control interfacial properties that minimize optical losses. Moreover, it should also be noted that, as explained above, the native oxide layer as well as hydrocarbons and any other contaminants may cover the scintillator surface prior to coating. The oxidized scintillator surface can change the electrical properties of the sensor. To this end, in the present invention, the material composition of the coating material bordering the scintillator surface may be selected to be _{an O 2 -scavenger that sucks oxygen from the underlying layers.} In this way, the deterioration of the optical efficiency of the sensor is minimized.

Minimization of such dynamic effects provides a uniform non-degraded efficiency of the sensor over time. Because of the physical properties of the scintillator material and its growth method, a semiconductor scintillator material (eg, single crystal or multiple quantum well) contains surface states and defects that create electron traps. The following may be a physical explanation of the cause of such effects. Defects, when charged, can create localized potential barriers to charges and become non-radioactive recombination sites (heating centers). Defects can behave as traps, depletion volumes, non-radiative recombination centers, and localized heating, and are susceptible to expansion or proliferation under strong excitation (eg, e-beam irradiation). These electron traps create a local potential (i.e., the potential rises in both the conduction and valence bands), creating a repulsion of free electrons, which in turn can create a localized depletion layer. The depletion layer can locally reduce the carrier density, thereby reducing radioactive recombination and total efficiency, and also promote the dynamic effects described above. As explained above, surface conditions can create a dynamic effect of changes in cathodic intensity and reduce the lifetime of the sensor. The inventive technique mitigates these effects (eg, by neutralizing these surface conditions), thereby increasing the efficiency and uniformity of efficiency of the sensor, and the lifetime of the sensor. The multi-coating structure can be made of at least two materials with different physical properties. In this regard, it is understood that if a single coating layer is used to reflect the emitted photons towards the scintillator structure, this single coating layer must be made of a material with a sufficiently high reflection coefficient to efficiently reflect the photons back. It should be. However, materials with high reflection coefficient do not have the desired physical and chemical properties to mitigate the lifetime effect described above. Moreover, such materials may not have good electrical contact with the scintillator material, so that the surface conditions created at the surface of the scintillator material are not neutralized. Thus, in some embodiments, the selected material(s) should have good ohmic contact with the defective cores, which neutralizes the charge in the defective cores, extending to the surface of the scintillator material. This in turn flattens the dislocation around the defect and prevents or lowers the formation of new traps.

Moreover, the coating materials used with the scintillator semiconductor materials cause a chemical reaction at the interface between the coating material and the semiconductor material. In such cases, an intermediate layer, which is generally non-conductive, can be created to reduce the efficiency of the sensor. The inventors have found, surprisingly, that the introduction of an additional coating material at the interface with the semiconductor scintillator material increases the lifetime of the sensor. The sensor of the present invention has an increased lifetime and stable cathodic light emission during operation, with minimal impact on sensor efficiency.

In the specific non-limiting example of FIG. 2D, the multi-coating structure 14 is made of at least two layers. The multi-coating structure 14 is configured and operable to reflect photons emitted by the active layer back towards the scintillator structure 12. The multi-coating structure 14 is also constructed and operable to mitigate the life effect. Specifically, its multi-coating structure can be configured to avoid the reduction of radioactive recombination and associated dynamic effects mentioned above. Controlling the quality and properties of the interface between the coating and the scintillator structure provides stable and uniform cathodic emission during operation. For example, it provides good electrical (e.g., ohmic) contact with the scintillator material to mitigate the effect of surface conditions, defects, and electron traps (e.g., neutralize surface conditions at the surface of the scintillator structure). It can be implemented by providing a material having. Accordingly, the multi-coating structure 14 can be configured and operable to minimize both the gradual deterioration of the cathodic light emission of the scintillator structure 12 and the dynamic change in cathodic light emission during the operation of the sensor 10 ′. . In some embodiments, the multi-coating structure 14 is made of at least one conductive material such that the multi-coating structure can serve as an electrode that applies an electric potential to the sensor. In this particular non-limiting example, the multi-coated structure 14 has at least two different physical and chemical properties, such as reflection coefficients, conductivity, and other chemical properties in a specific wavelength range of the emitted photons. And four different coating materials 14A and 14B. In certain non-limiting examples, the reflection coefficient of one coating material is about 0.5 for a particular wavelength emitted from the scintillator and >0.9 for a second coating material. For other materials that provide the same properties that mitigate the lifetime problem and the ionic problem, these values may be different (eg, 0.8 for the first coating material and >0.9 for the second coating material). The first reflective material 14A borders the scintillator structure 12, and the second reflective material 14B borders the electron emission from the object. The first reflective material 14A has a lower reflection coefficient than the second reflective material 14B. In this regard, it should be understood that the second reflective material 14B is chosen to reflect back photons emitted by the scintillator structure 12 in an efficient manner. Accordingly, the first reflective material 14A reflects some of the photons (from the scintillator) back to the scintillator structure 12. For example, the photons 73 emitted by the scintillator structure 12 propagate toward the light guide 50 included in the charged particle beam column (shown in FIG. 3). The figure also shows photons 71 that are emitted toward the first reflective material 14A by the scintillator structure 12 and, in addition, are redirected from the first reflective material 14A toward the scintillator structure 12. Shows. The second reflective material 14B is configured to reflect photons passing through the first reflective material 14A toward the second reflective material 14B back toward the scintillator structure 12. To illustrate, photons 72 are emitted from scintillator structure 12 toward first reflective material 14A and propagate toward second reflective material 14B. The second reflective material 14B redirects the photons 72 toward the scintillator structure 12 (and the light guide 50) through the first reflective material 14A. The higher reflection coefficient of the second reflective material 14B causes most of the photons to be reflected back towards the scintillator structure 12. However, a reflective material with a high reflection coefficient does not alleviate or solve the above mentioned lifetime problem. The reflective material 14A is a reflective material, rather than the reflective material 14B at the virtual interface between the reflective material 14B and the scintillator structure 12, which may have created a less conductive intermediate layer as described above. It has a better electrical (e.g., ohmic) contact at the interface between 14A and the scintillator structure 12. Certain physical properties (eg, contact properties) of the scintillator structure 12 actually neutralize the physical mechanisms that cause the scintillator's degradation and dynamic effects. In this way, the lifetime of the sensor is extended while the dynamic change of cathode ray emission during the operation of the sensor is minimized, and uniform efficiency of the sensor over time is provided. Note that, as explained above, due to the deterioration of the scintillator material, for example after 6 months, the efficiency of conventional sensors based on the scintillator material known in the art is much lower compared to the first frame taken on the first day. It should be. Accordingly, the efficiency of conventional sensors based on the scintillator material is non-uniform and cannot be accurately predicted and thus cannot be compensated accordingly. However, surprisingly, by using the sensor of the present invention, the minimization of the dynamic effects mentioned above results in an increase in photon radiation. Due to the multi-coating structure, the efficiency of the sensor of the present invention is uniform.

For example, at least one coating material can be made of a metallic material. In certain non-limiting examples, the multi-coating structure 14 is titanium, aluminum, nitride, gold, silver, molybdenum, titanium aluminide, palladium, tungsten, indium tin oxide, zirconium diboride, chromium, platinum. , Vanadium, and hafnium may be made of at least two.

In some embodiments, the first reflective material 14A and the second reflective material 14B are layers having the same thickness. In certain non-limiting examples, the first reflective material 14A can be made relatively thin (e.g., in the range of about 3-20 nanometers, e.g., 15 nanometers) due to the lower reflection coefficient. have. The second reflective material 14B can also be made relatively thin (eg, in the range of about 3-20 nanometers, for example 15 nanometers). However, the thicknesses of the first and second reflective materials must be large enough to reflect some of the photons from the scintillator back to the scintillator. Alternatively, the first reflective material 14A and the second reflective material 14B are layers having different thicknesses.

Reference is made to FIG. 3 which illustrates a system 100 to be used with the sensor of the present invention for detection of electrons emitted from an object. For example, system 100 may be at least a portion of a scanning electron microscope (SEM) or any other electron beam inspection tool. System 100 includes a mechanical unit 130 for supporting and moving an object 200. The system 100 also includes a charged particle unit, such as a charged particle beam column 120, operated at a specific column and wafer voltage. The charged particle beam column 120 is configured to irradiate an object with photons and detect charged particles emitted from the object 200. The charged particle beam column 120 includes a sensor S of the present invention, which may be implemented by a sensor (10 in FIG. 1D or 10' in FIG. 2D). The configuration of the system 100 is a specific non-limiting example, and the sensor S can be placed in any suitable location depending on the system requirements. The present invention is not limited to this configuration. The sensor S is exposed to charged particles emitted from the object 200 and emits photons of a specific wavelength range when charged particles having a specific collision energy collide with each other by cathode ray emission. The sensor S may be associated with the light guide 50 and the photomultiplier tube 60 included in the charged particle beam column 120. The light guide 50 is located between the sensor S and the photomultiplier tube 60. The charged particle beam column 120 is operated at a specific column and wafer voltage to allow photons emitted by the scintillator structure to propagate toward the light guide 50. Photons emitted in a direction different from the direction toward the light guide 50 must be redirected toward the light guide 50. Thus, the sensor S is also configured to reflect photons towards the scintillating structure and further towards the light guide 50.

4 is an example of a method 300 for detection of electrons emitted from an object. The method 300 includes, at 310, receiving electrons by the scintillator structure, and at 320, emitting photons due to the reception of the electrons. The step of emitting photons at 320 is followed by reflecting photons that have passed through the coating structure toward the scintillator structure at 330. The interface between the scintillator structure and the coating structure is configured and operable to control interfacial properties. Method 300 may include, at 340, substantially preventing negative ions from reaching the scintillator. Such practical prevention includes preventing all negative ions from reaching the scintillator, or just preventing most of the negative ions (e.g., 80%, 90%, 95%, 99%, etc.) from reaching the scintillator. can do.

5 is an example of a method 400 for increasing the lifetime of a sensor for detection of electrons emitted from an object. Method 400 provides, at 410, a scintillator structure having an active region bounded by the multi-coating structure, wherein the multi-coating structure is configured to reflect back photons emitted by the active region, at 420. , Controlling the properties of the interface between the active region and the multi-coating structure, and at 430, the gradual deterioration of the cathodic emission efficiency of the active region, and the cathode ray occurring during operation of the sensor and advancing throughout the life of the scintillator. Minimizing both dynamic changes in luminescence, thereby increasing the lifetime of the sensor. Method 400 may further include, at 422, selecting materials of the multi-coating structure to provide good electrical contact (ohmic contact) with the scintillator material. The method 400 may further include, at 432, removing the interaction of the anions with the scintillator structure. To this end, method 400 may further include, at 434, selecting a thickness of the multi-coating structure. For example, the thickness of the multi-coating structure can be increased.

Claims (13)

As a sensor for detecting electrons emitted from an object,
A scintillator structure having an active region and a specific lifetime ― The scintillator structure includes a high-speed scintillator material configured and operable to emit photons of a specific wavelength range upon collision of electrons of a specific collision energy by cathodoluminescence. Ham -; And
And a coating structure bordering the scintillator structure and exposed to electrons emitted from the object, wherein the coating structure is configured and operable to maintain a uniform potential across an interface between the active region and the coating structure. And, the coating structure may collide with the coating structure while at least reducing the interaction of a specific material composition selected to reflect photons emitted by the active area back towards the active area, and the anions interaction with the active area. A sensor for detection of electrons emitted from an object, having a specific thickness selected to minimize the loss of electronic energy at the time. The method of claim 1,
The scintillator structure includes a semiconductor group III-V multiple quantum well structure, a sensor for detecting electrons emitted from an object. The method according to claim 1 or 2,
The sensor is used with a charged particle beam column operated at a specific column and wafer voltage, and the specific thickness is determined by the energy at which the negative ions interact with the active region according to the specific column and wafer voltage, and emitted from an object. Sensor for the detection of electrons that are being damaged. The method of claim 3,
The thickness is selected according to the type of negative ions damaging the active area, a sensor for detection of electrons emitted from an object. The method according to any one of claims 1 to 4,
The coating has a thickness of at least 200 nm, a sensor for detection of electrons emitted from an object. The method according to any one of claims 1 to 5,
The specific material composition allows the detection of electrons emitted from an object, wherein the coating structure comprises a conductive material configured and operable as an electrode applying a potential that accelerates secondary and backscattered electrons towards the sensor. For sensors. The method according to any one of claims 1 to 6,
The coating structure comprises a multi-coating structure, wherein the multi-coating structure has different physical and chemical properties along the depth of the multi-coating structure. The method of claim 7,
The multi-coating structure comprises at least two different coating materials having different reflection coefficients in a specific wavelength range of the emitted photons. The method according to claim 7 or 8,
The multi-coating structure is made of at least two layers, a sensor for detection of electrons emitted from an object. The method of claim 9,
The two layers have different thicknesses, a sensor for detection of electrons emitted from an object. The method according to any one of claims 7 to 10,
The multi-coating structure includes a first reflective material bordering the active area, and a second reflective material bordering electron emission from the object, and the first reflective material is more than the second reflective material. A sensor for the detection of electrons emitted from an object with a low reflection coefficient. The method of claim 11,
The first reflective material bordering the active area is selected to enable good ohmic contact to mitigate the effect of at least one of surface conditions, defects, and electron traps. Sensor for detection. The method according to any one of claims 7 to 12,
The multi-coating structure is a specific material composition selected to minimize both the gradual deterioration of the cathode ray emission efficiency of the active region and the dynamic change in cathode ray emission that occurs during operation of the sensor and progresses throughout the life of the scintillator. And a sensor for detection of electrons emitted from an object having a specific thickness.

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